In general, nitrophenol (mainly o- or p-isomer) has been hitherto obtained by reacting phenol with nitric acid in sulfuric acid medium [for example, U. Al-Obaidi and R. B. Moodie, J. Chem. Soc. Perkin Trans. II, 467 (1985)].
However, when this method is applied to a halogenated phenol compound, particularly a phenol compound substituted with bromine, substitution, isomerization, disproportionation and the like occur and the nitrated product becomes a mixture thereof with by-products such as isomers, debrominated products and the like, which results in a low yield.
Under these circumstances, in order to establish a process for producing a nitrophenol compound in a good yield with less by-products which is advantageous from the industrial viewpoint, the present inventors have intensively studied a method for nitrating a phenol compound to convert into a corresponding nitrophenol compound. As the result, it has been found that the objective nitrophenol compound can be obtained in a good yield by reacting a p-bromophenol compound with nitrous acid in a mixed solvent of water and water-insoluble or slightly soluble organic solvent. That is, according to the present inventors' knowledge, in such a nitration reaction, when a phenol compound is reacted with nitric acid in sulfuric acid medium according to a known method, the yield of the objective nitrophenol compound is low. However, it has been surprisingly found that a nitrophenol compound can be selectively produced in a high yield by reacting the phenol compound with nitrous acid in a mixed solvent of water and a water-insoluble or slightly soluble organic solvent.
Canadian Patent Specification No. 777,124 issued on Jan. 30, 1968 discloses that a 2,6-di-tertiary-alkylated 4-nitrophenol is obtained by causing diluted aqueous nitric acid to act on a solution of the corresponding di-tertiary-alkyl-phenol in a water-insoluble organic solvent, but there is no disclosure about the reaction of a p-bromophenol compound with nitrous acid in the specification.
In Collection Czechoslov. Chem. Commun. 29(6), 1374-1379 (1964) and Z. Anal. Chem., 199(4), 276-290 (1964), J. Gasparic discloses the reaction of o-bromophenol compound with nitrous acid in a slightly acidic medium, but does not disclose the use of a water-insoluble or slightly soluble organic solvent.